Malignant Brenner tumor of the ovary: radiologic and histopathologic correlation demonstrating benign-to-malignant transition

Malignant Brenner tumors of the ovary are extremely rare, and imaging features remain poorly characterized. We report a rare case of a malignant Brenner tumor of the ovary with both extra-cystic and intra-cystic solid components. Magnetic resonance imaging and computed tomography revealed a left ovarian cystic mass with two distinct solid components: an extra-cystic solid component showing low T2 signal, minimal enhancement, no diffusion restriction on magnetic resonance imaging and dense and amorphous calcifications on computed tomography, and an intra-cystic solid component with heterogeneous T2 signals, strong enhancement, diffusion restriction on magnetic resonance imaging and no calcifications on computed tomography. These findings suggested a mixed tumor comprising benign and malignant elements. Surgical resection confirmed that the extra-cystic solid component was consistent with a benign Brenner tumor. The intra-cystic solid component exhibited decreased fibrous stroma and increased cellular density along with focal stromal invasion. These findings led to the diagnosis of a malignant Brenner tumor. Retrospective review identified a continuous band-like low T2 signal connecting the two solid components, corresponding to histologic transition from benign to malignant tissue. Recognition of this transition zone may aid in the diagnosis and differentiation of malignant Brenner tumors from other malignant ovarian neoplasms.